This invention relates to an improved grounding system for fixtures supporting elements in a processing line and particularly for coating of small parts.
Various items and parts are processed through an electrically conductive fluid medium for treating, coating or otherwise acting thereon. In a practical system for processing, and in particular for coating or painting parts and particularly small parts, the parts are placed in an apertured container, such as a barrel, which is supported for placement in a series of separate treating containers or tanks for pretreating, coating and finally curing of the coated parts. Various systems have been proposed in which the small parts are placed in apertured barrels. The barrels are mounted in a processing line for sequential immersion in a series of tanks including liquids for treating of the parts prior to applying a desired coating and a subsequent curing of the coating. An automated processing system is disclosed in U.S. Pat. No. 5,012,918 issued May 7, 1991. The patents illustrate application to individual large parts, but has been now applied to barrel processing by providing of a rotating barrel structure specially supported for passing through the line, as more fully developed hereinafter.
The processing system provides for stepped movement through a coating apparatus of a series of in-line processing tanks. As generally disclosed in the above patent, a series of like-mounted barrels are mounted to a support and passed in steps through the system. The tanks are spaced such that a series of the supported barrels are moved a corresponding length, moving between stations during each cycle. During each cycle, selected barrels or all barrels may be lowered into the aligned tank for appropriate treatment for a fixed period after which the barrels are raised, moved another step into alignment with a subsequent processing tank. Thus, the barrels are releasably mounted within a stepped conveyor with appropriate means to lower and raise the barrels as they are aligned with the respective stations. The processing apparatus provides for removing of the barrels at the exit end during one treating cycle and providing for the addition of a new load at the entrance end during the same treating cycle.
The system thus provides for the continuous stepped in a line operation and treating of parts in the barrels.
With present technology in certain coating processes the barrels must be connected to common ground within the processing apparatus.
Presently, the barrel must be specially constructed to provide for grounding of the barrel at each station or selected stations for immersion within the liquid such as for electrotreating, electroplating, and for electrocoating of the parts. The barrel are presently connected through a special ground connection.
Various grounding systems are presently available. For example, a gear train secured to the shaft with an outer gear connected to a ground path. A hollow shaft with a grounded wire secured within the shaft in sliding engagement therewith has been proposed. A prior art coating support assembly or unit has been constructed including a rotating conductive shaft with a non-conductive chain and sprocket unit secured to one end support and a separate conductive bushing unit connected as a second support. The bushing unit is shorter than the non-conducting chain support and located above the first end. A cup-shaped portion or member on the part to be coated is aligned with and covers the conductive bushing unit and as the assembly is lowered into the liquid, an air cavity is created about the bushing unit and prevents liquid engaging of the bushing unit, and maintaining the ground connection. Other suggested systems have included exposing a part of the barrel above the liquid and applying a grounding shoe. The shoe would require a rough surface to insure grounding through paint on the barrel, which would cause potential wear of the shoe and barrel. It could also scratch paint off which would fall into the e-coat tank. However, all such units when immersed in the paint, require frequent and costly cleaning, paint removal and general maintenance.
In current practice for coating small parts, the parts are placed in barrels or baskets which are removed from the system for curing to avoid coating of the barrel or basket.